Give him an actual script to work with, such as the old-guy buddy-comedy “Last Vegas,” and I’m even more likely to be charmed. The new movie also has Kevin Kline, Robert DeNiro and Michael Douglas, three other actors who have so mastered the art of being watchable that legions of us have found something redeeming in a flat-out terrible movie because one or more of them were in it. When you add all four of them together and give them a harmlessly pleasant script to work with, it would have been defying statistical probability for the results not to be at least mildly entertaining.

And when the four are determined to be as charming and thoughtful as we all know they can be, they elevate that pleasant script into a sweet, surprisingly funny Vegas vacation. The actors seem to both be relaxed and sincerely enjoying themselves, imbuing the movie with a sense of lightness and fun that transmits easily through the screen.

The four men play lifelong friends from childhood, first shown as 12-year-olds in a brief flashback scene before the movie shoots ahead 58 years. The plot, which involves Michael Douglas’s character getting married to a woman less than half his age, is really just an excuse to get the four friends back together and heading to Sin City. Other plot conveniences follow, all entirely harmless and designed solely to give the cast and crew more interesting toys to play with.

Kevin Kline gets the most ribald of the subplots, a condom and a weekend pass from his wife to have one wild night in Vegas in the hopes that it will give him his spirit back. It’s an idea that could be potentially icky in the wrong hands – say, if this was a geriatric version of “The Hangover” – but Kline embraces it with a hopelessly dorky enthusiasm that makes it funny instead of gross. By the end of the movie, it actually becomes heartwarming.

Morgan Freeman has little to do here but be Morgan Freeman, but as usual he does the job magnificently. The script does help the process along by giving him plenty of opportunities to be funny, and Freeman’s wide-eyed, knowing delivery surprised quite a few laughs out of me by the end of the movie.

DeNiro and Douglas carry more of the movie’s emotional weight. The two have been divided by a funeral and a lifelong secret, but their genuine love for each other shines through. The two men have both had roles where they’ve let themselves become more of a joke than a real person (I’m looking at you, DeNiro), but here their usual ticks are softened and rounded out by full measures of dignity and warmth. They seem like real, likeable human beings, and when they hurt, you hurt for them.

And when they pretend to be mobsters from back east or talk their way into judging a bikini contest, you laugh even though you probably shouldn’t. When the company is as good as it is in “Last Vegas,” it’s best to not think too hard and just let yourself enjoy the moment.